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Comparison of the accuracy of two different modes of continuous cardiac index measurement following rapid volume infusion

Christoph Wiesenack, MD^*, Christoph Fiegl^*, Andreas Keyser, MD^*, Sven Laule, MD, Christopher Prasser, MD^* and Cornelius Keyl, MD

^* University Hospital of Regensburg, Regensburg, Germany
Heart Center Bad Krozingen, Bad Krozingen, Germany, E-mail: christoph.wiesenack{at}klinik.uni-regensburg.de

To the Editor:

Despite the current debate about the usefulness of the pulmonary artery catheter (PAC),¹ cardiac index (CI) assessment by the thermodilution technique remains a frequently used technique.² A PAC with a rapid-response thermistor provides nearly continuous assessment of CI (CCI) and eliminates measurement variability associated with the intermittent bolus technique. We compared the accuracy of two different operation modes of CCI assessment (TREND mode, CCI_TREND and STAT mode, CCI_STAT) with bolus thermodilution CI (CI_TD) measurement regarding their response to rapid volume infusion.

With approval of the local Ethics Committee and written informed consent, we studied 21 patients (17 males), aged 53 to 78 yr (mean, 65.7 yr) undergoing elective coronary artery bypass grafting. Following induction of anesthesia, a right heart ejection fraction catheter (CCOmboV 774HF75; Edwards Lifesciences, Irvine, CA, USA) was inserted and connected to the Vigilance monitor system (Edwards Lifesciences,) for CCI and intermittent CI_TD measurement. The methodology of CCI measurement based on the pulsed warm thermodilution technique has been previously described in detail.³ CCI_TREND reflects an average flow over the previous six to ten minutes and is updated every 30 to 60 sec. CCI_STAT does not contain a moving average filter but depends on some previous data for artefact suppression, and is also updated every 30 to 60 sec. Hemodynamic measurements were performed simultaneously after induction of anesthesia, when CCI_TREND had stabilized (T1) and following volume replacement by infusion of 6% HES 200/0.5 (7 mL·kg^–1) with a rate of 1 mL·kg^–1·min^–1 (T2).

In all patients fluid challenge caused an increase in CI_TD (range 5.9% to 69.2%). The bias between CI_TD–CCI_TREND was 22.2% with a precision (SD of bias) of 17.8%, and the bias between CI_TD–CCI_STAT was 0.86% with a precision of 18.2%, respectively. The relative error, defined as 100{(CI_TD–CCI)/[(CI_TD+CCI)/2]}, was within 15% for just 27 out of 42 comparisons between the pooled data of CI_TD and CCI_TREND, compared with 40 measurements within 15% between the pooled data of CI_TD and CCI_STAT.

These results suggest that CCI_TREND failed to identify dynamic changes in hemodynamics caused by rapid volume application. CCI_TREND underestimated the increase in CI_TD following fluid challenge by more than 20% (Figure A), whereas CCI_STAT showed good agreement in CCI assessment at all timepoints of measurement (Figure B). Comparable results were observed by other authors during acute hemorrhage⁴ or following an increase in pacing rate.⁵

View larger version (17K): [in this window] [in a new window]   FIGURE Bland and Altman plot for comparison between cardiac index with bolus thermodilution (CITD) and continuous assessment of cardiac index and TREND mode (CCITREND) (A) and between CITD and continuous cardiac index and STAT mode (CCISTAT) (B) for percent differences. The solid line represents the mean difference (bias) and the dashed lines represent the limits of agreement (mean difference ± 2SD of the difference).

References

1 Sandham JD, Hull RD, Brant RF, et al. A randomized, controlled trial of the use of pulmonary-artery catheters in high-risk surgical patients. N Engl J Med 2003; 348: 5–14.[Abstract/Free Full Text]

2 Jacka MJ, Cohen MM, To T, Devitt JH, Byrick R. The use of and preferences for the transesophageal echocardiogram and pulmonary artery catheter among cardiovascular anesthesiologists. Anesth Analg 2002; 94: 1065–71.[Abstract/Free Full Text]

3 Yelderman M, Quinn MD, McKown RC. Thermal safety of a filamented pulmonary artery catheter. J Clin Monit 1992; 8: 147–9.

4 Poli de Figueiredo LF, Malbouisson LM, Varicoda EY, Carmona MJ, Auler JO Jr, Rocha e Silva M. Thermal filament continuous thermodilution cardiac output delayed response limits its value during acute hemodynamic instability. J Trauma 1999; 47: 288–93.[Medline]

5 Lazor MA, Pierce ET, Stanley GD, Cass JL, Halpern EF, Bode RH Jr. Evaluation of the accuracy and response time of STAT-mode continuous cardiac output. J Cardiothorac Vasc Anesth 1997; 11: 432–6.[Medline]

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